The present invention relates to a method and apparatus for communication between an electrical device and a switch for operating the device in general, and more particularly to communication means for centrally controlling the operation of a plurality of electrically operated devices.
Devices for transmitting data to and from an electrical device for activating or turning off the device are known in the art. These generally include a separate communication line laid between the device and the switch, or other means of activating the device.
Most of the conventional means for centrally controlling the operation of electrically operated devices can be divided into two groups:
control means utilizing an extra set of electrical conductors, or control lines, for each device, for the transmission of a control signal from the control means, such as a switch, to the controlled device or to its switching means.
control means employing electromagnetic radiation such as radio frequency (RF), or infra-red (IR), for the transmission of control signals from the control means to the controlled device or to its switching means.
These conventional control means suffer from several drawbacks. The use of special control lines for the transmission of control signals to each controlled device is cumbersome, and necessitates expensive laying of the control lines. Furthermore, changes in the location or of the type of a controlled device usually necessitate re-laying of its control lines.
IR transmission requires a line of sight transmission between the location of the device generating the control signal and the controlled device.
RF transmission, while not requiring line of sight between the control means and the controlled device, is often undesirable because the RF radiation is known, at times, to reach and actuate other devices, perhaps located elsewhere, in addition to actuating the intended one. Also, RF radiation is often blocked by metallic objects and therefore RF signal communication between the control means and the controlled device is not guaranteed.
It is also known to add signals to an existing wave on a power line. Communications data are modulated onto the electric wave. This method is complicated, requires additional circuitry and suffers from the same drawbacks as the RF transmission.
The following prior art patents provide control signals over an existing wave of a power line, but all suffer from deficiencies that make them inefficent or inappropriate: U.S. Pat. No. 4,719,446 to Hart; U.S. Pat. No. 4,222,035 to Lohoff; U.S. Pat. No. 5,493,267 to Ahlse et al; and U.S. Pat. No. 5,923,271 to Santini.
It is therefore desirable to provide means for controlling the operation of electrical devices that do not suffer from the aforementioned drawbacks.
According to the present invention, tie is provided a method and apparatus for communication of information along electrical conductors of electric power lines in general, and more particularly, means of communication between a central controller and a plurality of electrical devices.
There is thus provided in accordance with the invention, a method for generating and transferring control messages between a switch and an associated load coupled by an electric conductor power line, the method including modifying at least a portion of the shape of an electric power wave supplied on the electric conductor, without adversely affecting operation of the load.
According to one embodiment of the invention, the step of modifying the shape of an electric wave includes cutting at least a portion of the electric power wave supplied to the load.
According to another embodiment of the invention, the step of modifying the shape of an electric wave includes cutting at least one complete half-wave of the electric power wave supplied to the load.
According to a preferred embodiment the method further includes coupling a load controller between the conductor and the load, receiving the control messages in the load controller, and activating the load in accordance with the messages received.
Further according to a preferred embodiment, the method further includes coupling a central controller between the switch and the load controller, receiving control messages indicating a change of state from the switch in the central controller, and supplying control messages by modifying at least a portion of an electric power wave over the electric conductor to the load controller, in accordance with the messages indicating a change of state.
There is also provided in accordance with the present invention an apparatus for transferring command messages to a load including a controller for modifying an electric power wave supplied to the load on an electrical conductor of an electric power line.
According to a preferred embodiment of the invention, the means for modifying includes means for cutting at least a portion of the electric power wave.